Molded articles, and particularly blow molded structures such as bottles are commonly formed from polymers of 1-olefins such as polyethylene. It is important to the commercial utilization of a given polymer system that the converted product such as a bottle exhibit an optimized balance of properties, including for example, acceptable stress crack resistance and flexural stiffness. In addition, and in a contributing sense, it is necessary that the polymer exhibit suitable processability, i.e., satisfactory rheological behavior under flow and formation during fabrication. Although the viscoelastic behavior of polymer melts has been the subject of considerable study, it has not proven possible to translate performance during fabrication to end use articles in such manner as to selectively determine polymerization and particularly catalyst requirements. Moreover, as in any case catalyst performance must also be measured in terms of efficiency or productivity and stability over a sensible life.
The use of chromium compounds in the polymerization of olefins is well-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of CrO.sub.3 supported on an inorganic material such as silica, alumina or combinations of silica and alumina and activated by heating at elevated temperatures to polymerize olefins. When these catalyst systems are used in various polymerization processes such as the well-known particleform process, the resins produced, while useful in many applications, are unsatisfactory for others because of a deficiency in certain properties such as melt index.
Improved chromium based supported catalyst are known, particularly those disclosed and claimed in U.S. Pat. No. 3,984,351. Preferably, such catalysts employ an aluminum dopant i.e., the porous support is treated with an aluminum compound reactive with surface hydroxyl groups on the support, prior to heat activation, as disclosed in U.S. Pat. No. 3,985,676.
It has now been discovered that the aluminum compounds react with residual system water even at low levels, interfering with reproducibility in use in terms of resin properties. While this problem can be resolved by careful control of residual water level, as disclosed in copending and commonly assigned Ser. No. 800,586 of Rekers et al. filed concurrently herewith on May 25, 1977 reduction in moisture levels below about 0.4 weight percent in supports such as silica gel is difficult or expensive, and simpler and more direct methods would be of benefit for control of catalyst characteristics.
Accordingly, it is desired to identify aluminum compounds active to improve catalyst performance but essentially resistant to hydrolysis under preparative conditions, while preserving reactivity with the surface hydroxyl groups of the support materials.
Manyik et al. in U.S. Pat. Nos. 3,231,550 and 3,242,099 describe poly(hydrocarbylaluminum oxides) produced by the reaction of water with an organo hydrocarbylaluminum compound, which are in turn reacted with transition metal e.g., chromium compounds and used as olefin polymerization catalysts.
Rinse, and Rinse et al. in U.S. Pat. Nos. 3,054,816 and 3,056,725 show the preparation of polymeric aluminum oxide hydroxides mentioned as catalysts for dehydration and dehydrogenation of petroleum compounds.
Modifications in silica gel for catalytic activity are shown in Burwell, Chemtech, pp. 370-377 (1974) and Peri, J. Cat. 41, pp. 227-239 (1976). None of these prior art disclosures refer to a supported, polymeric hydrocarbon aluminate catalyst, or its use, as in conjunction with a chromium compound, in the polymerization of olefins.